The present invention relates to the Internet and other packet-based networks and more particularly to methods for wireless access to packet-based networks by mobile devices.
Support for wireless access between a correspondent node and a mobile device over the Internet is outlined in an Internet Engineering Task Force (IETF) proposal entitled xe2x80x9cIP Mobility Support,xe2x80x9d C. E. Perkinsxe2x80x94Editor, Request for Comments 2002 (October, 1996; hereinafter xe2x80x9cMobile IPxe2x80x9d). By utilizing Mobile IP, each mobile device is identified by a fixed home address and associated home agent, regardless of its current point of attachment to the Internet. Packets sent to a mobile device, from a correspondent node, are directed to the home agent. If the mobile device is away from home, the home agent forwards packets within an IP-in-IP tunnel to an assigned care-of address registered with the mobile device. Therefore, delivery of packets using Mobile IP for a mobile device away from home is accomplished utilizing a two-legged routing scheme. This two-legged routing scheme is known as triangular packet routing. Triangular packet routing is performed even if the mobile device away from home is serviced by the same subnet as the correspondent node with which it is communicating, thus resulting in an inefficient routing path for packet delivery.
Any IP addressing scheme has available a limited number of unique addresses. The assignment and use of multiple addresses per mobile device merely exacerbates the quandary associated with having a limited number of addresses.
The number of active packet routing address assignments is reduced and triangular packet routing is minimized by assigning a packet routing address to a mobile device accessing a wired subnet upon power up of the mobile device, and releasing the assigned packet routing address when the mobile device powers down. An address assigned in the manner described, and in accordance with the present invention, is called a dynamic permanent address. Dynamic permanent addresses are assigned directly by a Dynamic Host Configuration Protocol (DHCP) server or indirectly via a node acting as a DHCP relay for a DHCP server.
In an exemplary embodiment of the present invention, a domain is defined to incorporate an entire subnet which includes interconnected packet routers and wireless base stations for accessing the Internet from a mobile device. Therefore, a mobile device may access the Internet through a base station included within a home domain or a foreign domain. If attached to a base station included within the home domain, the mobile device utilizes only a single address, a dynamic permanent home address. If attached to a base station included within a foreign domain, the mobile device utilizes the dynamic home address and an additional care-of address. The mobile device""s home agent tunnels packets to the care-of address when the mobile device is away from home.
Utilizing a Dynamic Home Optimization, in accordance with an exemplary embodiment of the present invention, a mobile device is not registered with any domain as a home domain until the mobile device initiates a power up. Upon initial power up, the mobile device is assigned a dynamic permanent home address from the Dynamic Host Configuration Protocol (DHCP) server within the domain in which the power up occurs. This domain then becomes the home domain for the mobile device. If the mobile device subsequently changes its point of attachment to a base station included in a foreign domain, the mobile device is assigned a second IP address by the DHCP server servicing the foreign domain. This new second address is the mobile device""s care-of address. The mobile device retains its original IP address assigned in its home network, and packets are tunneled from the home agent in its home domain to the mobile device""s care-of address in the foreign domain. When the device is powered down, the mobile device relinquishes its dynamic permanent home address and the care-of address, allowing those addresses to be available for subsequent reuse. Upon the next power up, the mobile device is assigned a new dynamic permanent address in the domain it attaches to when it powers up.
Advantageously, the present invention""s use of dynamic permanent addresses allows for a given number of mobile users to access a subnet utilizing fewer IP addresses than required with a permanent registration type scheme, assuming that all mobile users are not powered up at the same time. Additionally, we have recognized that the mobility of a mobile user between base stations is typically a localized phenomenon. That is, the majority of handoffs occur between base stations which are each included within a common subnet or domain. Therefore, the majority of handoffs between base stations do not require a DHCP server to assign a new care-of address. The present invention leverages this knowledge by designating the domain which includes the base station to which the mobile device attaches upon power up as the home domain. Such a scheme offers two beneficial effects. First, the quantity of IP addresses utilized is further reduced, since only one IP address is required when the mobile device is attached to any base station included within the home domain, the home domain is the domain in which the mobile device powers up, and the majority of handoffs occur within a single domain. Second, instances compelling the use of triangular routing are less frequent since tunneling from a home agent is required only when the mobile device is attached via a foreign domain and the present invention enhances the probability that a mobile device will be serviced by base stations included within the home domain.